From The FAQs...For more See the link http://www.ewg.org/hair-straighteners/our-report/faqs-7/
Is there any chemical hair straightener that’s safe to use?
EWG hasn’t found a chemical hair straightener that we can recommend. Some brands claim to use chemicals that are less toxic than formaldehyde and less prone to cause allergic reactions. But these may require you to leave the product on for a day or two before rinsing, so you’re exposed to more of the chemical – you’re breathing more vapors, and more is soaking through your skin over time. Some “formaldehyde-free” products contain “formaldehyde releasers” that expose you to the chemical anyway. Most of the products we’ve reviewed don’t list their active ingredients, but almost all unlabeled products that have been tested have been found to contain substantial amounts of formaldehyde.
What other hair-care products should I avoid?
Perms and straighteners rely on chemicals to break the hair’s bonds, after which it reforms to a desired shape. You should avoid or be a very careful consumer of both perms and straighteners. We assess many of these products for safety and explain our concerns here: [For more information, click here.]. Minimize your use of dark hair dyes; many contain coal tar ingredients that have been linked to cancer in some studies. “Cold” permanent waves based on chemicals, not heated rollers, rely on some of the same chemicals used to straighten hair.